Device and method for fire detection in enclosed environments are suitable for storage rooms, silos, bunkers, and other enclosures, which are, among other things, subject to regulations on explosion protection and from which air is aspirated, checked for typical fire criteria and, if necessary, a fire alarm is triggered.
The present disclosure is especially suitable for enclosed environments such as silos or bunkers for combustible and/or dust forming bulk goods or storage areas for combustible materials from which air samples have to be taken for the purpose of using fire parameters to generate a fire alarm.
Enclosed environments in the sense of the present disclosure can be silos or bunkers as well as other storage areas and transport areas which are subject to explosion protection requirements and in which easily combustible material and dust forming bulk goods such as wood shavings, wood chips, wood pellets, grain, powdered fodder, fertilizer, or other such goods are stored or transported. An explosive air-dust mixture can form due to an appropriately high concentration of dust from these materials. Sources of ignition can then be, for instance, warm or hot parts or surfaces. In the following sections these enclosed environments are also referred to as storage areas. These storage areas/enclosed environments, which are subject to regulations for protection against explosion, are also referred to in the following sections as “ex-zones”. In the following sections, “dust” is understood to denote small particles of the materials which are being stored or transported/poured.
Discharge systems, conveyor belts, or processing devices are the primary potential sources of ignition in this context. Through friction or overheating of material being conveyed in the region of the discharge worm drive a deep lying fire can start in a silo or a storage area without being noticed. Ignition sources introduced from outside through the entry opening also constitute a fire hazard. In addition, spontaneous combustion can occur through biological decay processes in piled up materials. A smoldering fire that starts in this way can spread to the surface of the piled up material and, as a result of the access to oxygen, quickly develop into an open fire which destroys the entire storage area or machinery. The difficulty of detecting incipient fires in storage areas, bunkers, or silos is due to the fact that there is often a high proportion of fine dust and carbon monoxide or high relative humidity. Serious problems exist in such ex-zones regarding early detection of fires. Conventional fire detection systems without any technical modifications and without approval for use in ex-zones are not appropriate for use here.
Fire detection systems such as aspirating smoke detector systems with sensors/detectors for detecting fires which are installed to detect fires in ex-zones are required to satisfy the requirements for protection against explosions such as the set of standards EN 60079 or IEC 60079 or the appropriate national requirements such as NEC 500 to NEC 516. Such systems are not permitted to contain any parts which could become so hot that they constitute ignition sources.
Devices which meet these requirements are tested and approved by appropriate national certifying agencies. They are then recognized as devices or machines with ex-approval for specific classified ex-zones such as zones 20, 21 or 22. Devices with ex-approval are technically more complicated and are more costly in comparison with standard machines.
In EP 1 542 188 B1 a device and a method for detecting incipient fires is described according to which samples of air are continuously extracted from spaces or from electrical devices and tested for fire detection characteristics. In order to direct the air flow to be extracted, the aspirator opening must have a specified size and shape.
The filter is for keeping dust concentrations low. No provision is made for monitoring the filter for defects or the air flow for exceeding the explosion limit.
DE 197 81 749 T5 describes a system for monitoring the functioning of the dust filter of a fire detection system in areas which are not potentially explosive for blockage of the filter where, if a specified threshold value is exceeded, a warning signal is generated after which the filter is replaced.
DE 101 25 687 B1 describes a device for detecting fire sources or gas contamination in one or more monitored spaces which has a main detector for detecting a fire parameter value or a gas contamination level which is connected by means of an aspirating unit with a pipe fitted with an intake opening which is required in every space being monitored.
The devices described above are not suitable, nor are they permitted, in particular for cost-effective fire detection in enclosed environments which are subject to explosion protection regulations.
For fire detection equipment such as aspirating smoke detector systems without ex-approval, which extract and analyze air from such enclosed environments, it must be ensured that dust concentrations of the aspirated air-dust mixture sucked in the aspirating smoke detector system are below the limits of the maximum allowable concentration for a potentially explosive atmosphere.